Liberia confirmed a second case of Ebola on Tuesday just a day after authorities said they had detected a new case of the deadly virus previously thought to have been eliminated from the West African country, a senior health official said.

Liberia, once at the centre of the worst recorded Ebola epidemic in history, was declared Ebola-free by the World Health Organization on May 9 after going 42 days with no new infections.

The cross-border outbreak has killed more than 11,200 people since it began in December 2013. Twenty new cases were reported in the week to June 21 in Guinea and Sierra Leone.

"We have two confirmed cases today in Liberia," said Dr. Moses Massaquoi, case management team leader for Liberia's Ebola task force. He did not provide details of the new case.

The body of a 17-year-old boy from Margibi County, a rural area outside of Monrovia, was confirmed to be positive for the virus on Sunday and was buried the same day.

It is not clear how he was infected and the information was not made public until Tuesday.

Massaquoi said that tests were underway to establish whether there are further cases. Health officials say they isolated people who had contact with the teenager and are at risk of further infection.

A message from the Twitter account of the Liberian information ministry said that two people from the teenager's home had been confirmed as Ebola positive. It was not immediately possible to verify that information, nor was it clear if that included the case cited by Massaquoi.